Interannual variability in sea-ice thickness in the pack-ice zone off Lützow–Holm Bay, East AntarcticaInterannual variability in sea-ice thickness in the pack-ice zone off Lützow–Holm Bay, East AntarcticaInterannual variability in sea-ice thickness in the pack-ice zone off Lützow–Holm Bay, East Antarctica

Under the Japanese Antarctic Research Expedition (JARE) program, sea-ice thickness has been routinely monitored off Lützow–Holm Bay (East Antarctica) during the summer (mid-December to early January) since 2000/01, using an electromagnetic induction (EM) instrument onboard the icebreaker Shirase. Analysis of these data over a 10-year period, combined with visual observations using a simplified form of the ASPeCt (Antarctic Sea ice Processes and Climate) protocol, suggests a strong interannual variability in sea-ice thickness in this region. For the repeat pack-ice observation area, where the sea-ice thickness averaged over the nine seasons is ∼1.9 m, mean thicknesses of observed sea-ice in 2010/11 and 2011/12 are exceptionally large, at ∼3.3 and ∼5.8 m, respectively. This result is strongly related to regional patterns of sea ice dynamics. Ice convergence caused by anomalous northerly winds was particularly high in 2011/12, suggesting that the extremely thick ice observed in that season resulted largely from sea-ice deformation processes (including pressure ridging). Longer-term analysis of data from the past 34 years confirms that sea-ice conditions and thickness off Lützow–Holm Bay in summer are determined mainly by the large-scale pattern of atmospheric pressure in December.リュツォ・ホルム湾沖流氷域では、日本南極地域観測隊による夏期の海氷観測が2000/01年から行われている。10年間のEM観測と目視観測の結果を基に、この海域の海氷厚の経年変動を明らかにし、その要因を議論した。流氷域の中でも観測が集中していた海域においては、9年間の平均全氷厚が~1.9 mであったのに対して、2010/11年と2011/12年はそれぞれ~3.3、~5.8 mと例外的に厚く、大きな経年変動をしていたことが分かった。2011/12年は北風が卓越しており、海氷が北風によって岸や定着氷縁へ押し付けられ激しい海氷変形が起こり分厚い氷盤が形成されたと考えられる。過去34年間の大気再解析データから、リュツォ・ホルム湾沖の夏期の海氷状況や厚さは12月の気圧配置から大きな影響を受けていることも示した。